Vaccine Safety

Frequently Asked Questions

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Why do we still need vaccines if the diseases they prevent have disappeared from our part of the world?

Answer: It is important to continue vaccine programs for four basic reasons:

• First, unless a disease has completely disappeared, there is a real risk that small outbreaks can turn into large epidemics if most of the community is not protected. The only disease that has been entirely eliminated in the world so far is smallpox. Some diseases, such as tetanus, are caused by bacteria that live naturally in the soil. The risk of diseases like tetanus will never disappear, so continued immunization is important.
• Second, no vaccine is 100% effective. There will always be some people who are not immune, even though they have had their shots. This small minority will be protected as long as people around them are immunized.
• Third, there are a small number of people who cannot receive vaccines. These may be people who have previously had a severe allergic reaction to a component of the vaccine, or they have a medical condition that makes receiving vaccines too risky for them. These people are not protected from disease, and for some diseases it is very important that people around them are immune and cannot pass disease along to them. By protecting themselves, immunized people can also protect those around them who are vulnerable to disease.
• And fourth, most vaccine-preventable diseases are still common in other parts of the world. Travellers can carry them from country to country. If we are not protected by immunization, these diseases will quickly spread. For example, most cases of measles in Canada today can be traced to someone who travelled here from a country where measles is more common.
  

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